Article on Best Ab Exercises

Little bit old, but nice article on ab exercises by Bret Contreras

https://www.t-nation.com/training/inside-the-muscles-best-ab-exercises

Spoiler:
Based on this experiment, here are the top three exercises in terms of mean and peak activity for each muscle part:

Rectus Abdominis
Mean: Chin Up, Hanging Leg Raise, Ab Wheel
Peak:  Chin Up, Hanging Leg Raise, Swiss Ball Crunch

Internal Oblique
Mean: Ab Wheel from Feet, Ab Wheel from Knees, Bodysaw
Peak:  Ab Wheel from Feet, Bodysaw, Tornado Ball Slam

External Oblique
Mean: Ab Wheel from Feet, Hanging Leg Raise, Bodysaw
Peak:  Turkish Get Up, Hanging Leg Raise, Bodysaw

Erector Spinae
Mean: Kneeling Cable Lift, Landmine, Reverse Hyper
Peak:  Kneeling Cable Lift, Tornado Ball Slam, Lumbar Extension